Mystery Flights

Why did three experienced pilots fail?

February 1, 2010

Most short journeys begin well and end well. We make our preflight inquiries, look at the sky, perform our usual preflight checks, take off—and arrive. We know the route, the countryside, and the superintending air. Perhaps it’s a trip we have flown dozens of times. We exercise our skills, enjoy our routine, and often learn something new. And we have every expectation of success.

Yet sometimes things go awry. In the past few years, three highly experienced pilots perished in crashes for which there are no good explanations. One hit a cable a few feet above a river; two hit mountain slopes. Each fatal accident involved someone well known, a public personage. Each individual was an explorer in this realm of air. Each pilot had successfully balanced risk and adventure—until his last flight.

These pilots were on routine trips. Flight conditions were characteristic for the area. When fellow aviators examine the facts in each case, the reasons for the way each pilot conducted his flight are inexplicable, a mystery. The big question is: why?

On March 17, 2009, renowned mountain-flying pilot Sparky Imeson died flying a Cessna 180 between Helena and Bozeman, Montana. Imeson was 64. He was one of the first to codify mountain-flying principles and lore as he knew them. He had written several books on mountain flying; his most recent was Mountain Flying Bible. Imeson listed “Sparky’s 10 Commandments” for mountain flying, the last of which was: “Avoid becoming complacent. Do not fly by rote, ignoring the warning signs of weather, terrain, or wind.”

Imeson, who had 20,045 flight hours, held an airline transport pilot certificate and several flight instructor ratings. He departed Bozeman (elevation 4,474 feet msl) in the afternoon. His destination, about 60 miles to the northwest, was Helena (elevation 3,874 feet msl). Bozeman weather at the time showed an east wind at five knots with broken clouds at 6,000 feet. At the same time the Helena ASOS reported winds from 260 degrees at 18 knots gusting to 25, with a few clouds at 4,800 feet agl and an overcast layer at 5,500 feet.

A witness a couple of miles from the crash site, about halfway between the two cities, said that it was snowing in the mountains west of the accident site and that the wind was blowing about five to 10 miles an hour. The NTSB estimated the time of the crash at about 2:45 p.m.

A direct flight between Bozeman and Helena would have crossed mountains topping out at around 8,800 feet. Considering the cloud layers, Imeson had an easy route along the Missouri River, through broad valleys to the east of those mountains. He was not reported missing until evening. Two days later the wreckage was found on a steep hillside a few miles west of the river. Someone near the crash site had seen an airplane like the Cessna 180 flying north near some power lines. The wings were below the power lines. The witness, who thought the airplane was 20 to 30 feet above the ground, could see the tops of the wings as he watched the airplane do a steep pull-up into a 180-degree turn. The aircraft spooked some elk nearby.

Imeson’s airplane hit trees, knocking off the left wing, and then it struck the ground. The fuselage was consumed by fire. The total wreckage path was only about 600 feet long. The NTSB concluded that the aircraft hit trees and the ground in high-speed, controlled flight, and listed probable cause as the “pilot’s failure to maintain clearance from trees and terrain while maneuvering at a low altitude.”

With the difference in surface wind between Helena and Bozeman, it is safe to assume that the mountainous terrain between the two cities was generating downdrafts on the peaks flanking the Missouri Valley. And although he was out flying low at the base of the mountains, Imeson may have flown into a downdraft channeled into a place where he didn’t expect it. Flying fast and low, in combination with an unexpected downdraft, could have tipped his routine flight into disaster.

Steve Fossett crashed not far from Yosemite, in California’s Sierra Nevada range, on September 3, 2007, at about 9:30 a.m. He was 63 years old. On a pleasure flight, Fossett had taken off from a private strip near Yerington, Nevada (elevation 4,953 feet), about 8:30 a.m. He said he intended to fly the 180-horsepower, high-wing Bellanca Super Decathlon south to U.S. Highway 395, which flanks the Sierras near the Nevada/California state line. When Fossett did not come back after three hours, the search for him began. Despite exhaustive efforts, the wreckage was not found until October 2008, more than a year later.

The crash site was located about 65 miles south of the departure airport, east of the 13,000-foot Ritter Range and the jagged Minarets. Apparently the airplane was moving fast and hit about 300 feet below the top of a steep ridge that ran northwest/southeast. On the southwest slope, the debris field measured about 350 feet long and was oriented to the north. The NTSB concluded that the airplane had crashed right wing low in level flight. The aircraft was severely fragmented and burned, and the ELT was destroyed.

In attempting to trace Fossett’s route, an initial radar track that had been ruled out earlier because of an error in the time, turned out to be applicable. The track began at 9:07 a.m. and ended at 9:27, about a mile northwest of the crash site. The aircraft was traveling southbound over mountainous terrain about 10 miles west of U.S. 395. During the first few minutes of the track the altitude encoder reported altitudes of 14,500 to 14,900 feet. But most of the radar track indicated only a primary target with no altitude shown.

The NTSB compared crash site density altitude of 12,700 feet with theoretical downdraft calculations and ideal aircraft performance figures and concluded that the probable cause for the accident was the pilot’s encounter with downdrafts that exceeded the climb capability of the airplane.

The NTSB report did not include winds aloft forecasts for Reno, Nevada; Fresno, California; and Bishop, California, so it’s not known what information Fossett had before he took off that morning. About 9:30 that same morning, a pilot flying a King Air crossed the Sierra within 20 miles of the crash site. He stated that winds were calm on the surface but strong at 2,000 to 3,000 feet agl. He said that at 2,500 feet agl over the Sierra, winds had measured 30 to 35 knots from 240 to 290 degrees. The winds aloft were so strong that on his initial arrival into Reno, the pilot queried ATC whether surface winds at Reno really could be calm as ATC had reported.

The King Air pilot’s report of en route winds is significant because the wind direction was nearly perpendicular to the main axis of the Sierra. East of the crest of the range the winds would have tumbled over and through the valleys and pinnacles, in downdrafts and rotors. In addition, considering the very convoluted nature of the terrain, and morning atmospheric heating, there would have been up- and down-valley winds and flow reversals over the ridges near Fossett’s crash site. (See Mountain Meteorology by C. David Whiteman, Oxford University Press, 2000.)

Also that morning, before 10 a.m., people camping at 9,400 feet in the Sierras 30 miles north of the crash site saw an airplane heading south into the wind, toward Yosemite. The aircraft looked as though it was standing still because of the wind. On the ground at the campsite it had been very windy that morning. Later on, when one of the campers saw photos of the airplane on TV, he identified and reported the Decathlon as the airplane he had observed.

A mountain wave existed and it was decoupled from surface winds farther east. The sky over the mountains was clear. Lenticular and rotor clouds are signs of a mountain wave. If the atmosphere is dry, no clouds form—but the wave still exists. With actual winds aloft at 12,000 feet from the southwest at 35 knots the downdrafts on the east side of the Sierras could have been 1,000 to 2,000 feet per minute. Fletcher Anderson, in his text, Flying the Mountains, mentions that with 15-knot winds at mountaintop level a pilot can expect a 1,000-fpm sink rate on the lee side. And says: “Your small basic aircraft cannot possibly outclimb that sort of downdraft.”

Fossett had extensive experience as a glider pilot. He had made record wave flights out of Omarama, New Zealand, and soared to more than 50,000 feet over mountains in Argentina. So he knew about mountain winds, rotors, and downdrafts. In his flight south among the peaks Fossett was motoring along one of America’s best-known mountain wave areas, between Mono Lake and Bishop. He must have been aware of the hazards of local terrain and airflow. What was he doing there in a small basic airplane, practically standing still as he threaded his way through the peaks? How did he get into a situation where there was no way out? Perhaps the very fact that he had an engine in his aircraft made him more adventurous.

Fossett was well known as an adventurer who had made some astonishing record-breaking flights in sailplanes, jets, and balloons. His total flight time was more than 6,731 hours. His most recent recurrency training had been in a Cessna Citation X, but he had only about 40 hours in the Decathlon.

In Flying the Mountains, Fletcher Anderson discusses flying down canyons. About flying low in a canyon on search and rescue operations—possibly under bridges and power lines—he says: “This can be extremely exciting and very heroic, but how often do you actually need to be that low?”

Yet flying low was exactly what Anderson did. On November 18, 2005, at around 9 a.m., Anderson was flying a Civil Air Patrol Cessna 182R from Jackson, Wyoming, south to Afton, Wyoming, to conduct a CAP checkride. Along the Snake River Canyon highway, a woman who had been stopped by police saw an airplane flying down the canyon below the highway and treetops. She told the trooper what she had seen, and shortly after the officer found the Cessna upside down in the river about seven miles east of Alpine, Wyoming.

The airplane had hit a 7/8-inch-thick cable stretched across the Snake River. The cable hung from supports 30 feet above the river, was 324 feet long, and at its lowest point was about 25 feet above the river. The airplane hit the cable about 107 feet from its end. The NTSB faulted the pilot for an “intentional low-level flight/maneuver” as the probable cause of the accident; poor judgment was a contributing factor.

At Jackson (elevation 6,451 feet), the AWOS reported weather at time of departure as calm winds with a 1,400-foot ceiling. Crash site weather was clear and visibility unlimited. The straight-line distance between Jackson and Afton is around 60 miles, but rugged mountains up to about 10,000 feet block the way. Since there was a low ceiling at Jackson, Anderson chose to fly south along the Snake River. He was 57 years old and had logged 4,700 hours total time.

Three western states, big skies, big mountains. Three accomplished aviators, each flying fast, alone in single-engine aircraft. Two were professional pilots; the third was a highly credentialed adventurer. Each man was in good physical condition. No one had filed a flight plan. Their airplanes were operating properly. Regional weather was typical and familiar, and VFR.

According to the NTSB, Fossett’s wife characterized his excursion as “a Sunday drive”—not a flight that required the extreme concentration needed for record-breaking achievements. Imeson was observed apparently at play with the airplane, flying low near power lines, doing a steep pull-up into a 180-degree turn, maybe looking at elk. Anderson was speeding down a canyon just above the water, a thrilling excursion. Each man was supremely confident in his abilities. Each was experienced in mountain flying, coping with winds and rugged country.

So why did these formidably qualified aviators fly at high speed into terrain? What was going on in their minds when they went lower and lower, coming closer and closer to lethal obstacles?

Perhaps each pilot was creating adventure out of a routine flight by setting up challenges. Maybe that’s the common thread. Flying low and fast over undulating terrain, how quickly can I pull up and turn? Coursing down this canyon, how close to the trees and water can I get, how much space is there to anticipate that next twist in the canyon wall? Here amidst these stony gray peaks I’m at the limits of climb power and the vertical speed indicator spins backwards around the dial; how much room do I have to point the nose down and where is my escape route?

Despite the risks, we pilots always imagine adventure in terms of a successful outcome. When what’s necessary to finish a risky phase of flight shades from skill into luck, then adventurousness has gone too far.

Margaret Lamb, AOPA 317756, is a CFII and long-time Navion pilot who discovered and publicized mountain microscale weather as a factor in Colorado mountain flying crashes. She has lectured widely on reading clouds and flying mountain weather.